In common with about 80% of all plants, cotton forms VAM (vesicular-arbuscular mycorrhizas). VAM are associations of soil-borne fungi with the roots of plants. Presence of the fungi in the roots increases the uptake of mineral nutrients that diffuse slowly through soil, such as phosphate, zinc, copper, potassium and ammonium. The fungus spreads beyond the nutrient depletion zone surrounding the root and accesses the pool of nutrients in the soil. VAM fungi also influence the resistance of plants to drought stress and pathogens. V AM are mutually beneficial because the plant supplies the fungus with organic food.